An intracavity frequency-doubled fiber laser

Abstract

The application discloses an intracavity frequency-doubled fiber laser, which comprises a pump source, a light combiner and a bidirectional light amplifier, wherein a first optical fiber collimator, a first light polarization direction rotating device, a polarizer, a laser frequency-doubling device and a laser cavity mirror are sequentially arranged along an optical path on one side of the bidirectional light amplifier; a second optical fiber collimator, a polarization beam splitter, a second light polarization direction rotating device and a reflecting device are sequentially arranged along the optical path on the other side of the bidirectional light amplifier; the fundamental frequency laser output from the bidirectional light amplifier is rotated by 45 degrees by the first light polarization direction rotating device on one side and then enters the polarizer, and then enters the laser frequency-doubling device to be frequency-doubled and is output through the laser cavity mirror; the fundamental frequency laser is entered into the second light polarization direction rotating device through the polarization beam splitter on the other side, is rotated by 45 degrees and is incident on the reflecting device, is reflected back, is rotated by 45 degrees again, is entered into the bidirectional light amplifier through the polarization beam splitter. The application has the advantages of small size and low cost, and different waveband frequency-doubled lasers can be output by replacing devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, in particular to a cavity frequency-doubled fiber laser. BACKGROUND

[0002] At present, the nonlinear frequency conversion technology is that when the fundamental light is incident on the nonlinear optical crystal, the nonlinear effect is excited under the condition of satisfying the phase matching, thereby generating new band laser, which expands the wavelength range of laser light source. By laser frequency doubling, various wavelengths of laser light can be obtained, such as red light, green light, blue light, ultraviolet and deep violet light laser, etc. They have great application prospect and broad market in large screen laser display, laser medical treatment, high-density storage, microelectronics, micro-mechanical, laser holographic technology and pump adjustable optical parametric laser. Generally, visible light and ultraviolet laser are realized by cavity-in or cavity-out frequency doubling. The cavity-in frequency doubling has high conversion efficiency; the cavity-out single-pass frequency doubling has relatively simple structure, but low conversion efficiency. The fiber laser has high conversion efficiency, good beam quality, convenient thermal management, compact structure and easy maintenance, etc. It can be used as the fundamental light source of the cavity-in frequency-doubled laser, but the cavity-in frequency doubling usually requires that the laser can be polarization maintaining in the cavity, so the cost of the polarization maintaining fiber laser made of full polarization maintaining devices is relatively high when the frequency doubling is realized in the cavity. SUMMARY

[0003] The present application provides a cavity frequency-doubled fiber laser to solve the technical problems in the prior art.

[0004] The technical scheme adopted by the present application to solve the technical problems in the prior art is as follows:

[0005] A cavity frequency-doubled fiber laser, comprising a pump source, a light combiner and a bidirectional optical amplifier, wherein a first optical fiber collimator, a first optical polarization direction rotating device, a polarizer, a laser frequency doubling device and a laser cavity mirror are sequentially arranged along the light path on one side of the bidirectional optical amplifier; a second optical fiber collimator, a polarization beam splitter, a second optical polarization direction rotating device and a reflecting device are sequentially arranged along the light path on the other side of the bidirectional optical amplifier.

[0006] The first and second optical polarization direction rotating devices are used to rotate the polarization direction of the fundamental laser by 45° in a non-reciprocal manner.

[0007] The laser frequency doubling device is used to change the fundamental laser with a frequency of ω into a frequency-doubled laser with a frequency of 2ω after passing through the device.

[0008] The polarization beam splitter is used to divide the fundamental laser into S-polarized light and P-polarized light.

[0009] The pump light generated by the pump source is coupled to the bidirectional optical amplifier by the light combiner, and the bidirectional optical amplifier absorbs the pump light and generates, amplifies and outputs the fundamental laser.

[0010] The fundamental laser output from one side of the bidirectional optical amplifier is collimated by the first optical fiber collimator, enters the first optical polarization direction rotating device, is rotated by 45° by the non-reciprocal rotation, enters the polarizer, and the polarized fundamental laser in the same direction as the polarizer transmission axis passes through the polarizer and enters the laser frequency doubling device. Part of the polarized fundamental laser is converted into frequency-doubled laser and output through the laser cavity mirror; the polarized fundamental laser that is not converted into frequency-doubled laser is reflected back by the laser cavity mirror, sequentially passes through the laser frequency doubling device and the polarizer, and then enters the first optical polarization direction rotating device, and is rotated by 45° by the non-reciprocal rotation and then enters the bidirectional optical amplifier.

[0011] The fundamental laser output from the other side of the bidirectional optical amplifier is collimated by the second optical fiber collimator, enters the polarization beam splitting device, is transmitted by the polarization beam splitting device, enters the second optical polarization direction rotating device, is rotated by 45° by the non-reciprocal rotation, is reflected by the reflecting device, is folded back to the second optical polarization direction rotating device, is rotated by 45° by the non-reciprocal rotation again, and then sequentially passes through the polarization beam splitting device and the second optical fiber collimator and enters the bidirectional optical amplifier.

[0012] Further, the folded light path between the polarization beam splitting device, the second optical polarization direction rotating device and the reflecting device is a mouth-shaped path when the fundamental laser output from the bidirectional optical amplifier enters the polarization beam splitting device.

[0013] Further, the polarization beam splitting device is composed of a prism A, a parallelogram prism and a prism B which are sequentially attached from top to bottom, the cross sections of the prism A and the prism B are right-angled triangles or right-angled trapezoids, and the included angle between the inclined surface and the right-angled surface of the two is 45 degrees; the reflecting device is a 45° isosceles right-angle prism.

[0014] Further, the first optical polarization direction rotating device and the second optical polarization direction rotating device both include a Faraday rotator.

[0015] Further, the pump source, the optical combiner and the bidirectional optical amplifier form forward pumping or backward pumping or bidirectional pumping.

[0016] Further, the polarizer is a Glan prism or a polarization beam splitting prism.

[0017] Further, the laser frequency doubling device includes a frequency doubling crystal, and the matching mode of the frequency doubling crystal is type I critical phase matching.

[0018] Further, the polarization beam splitting device is a polarization beam splitting prism group or a pure yttrium vanadate crystal.

[0019] Further, the bidirectional optical amplifier comprises a gain optical fiber, and gain ions are arranged in the gain optical fiber, and the gain ions comprise any one or more of neodymium ions, erbium ions, germanium ions, praseodymium ions, holmium ions, europium ions, ytterbium ions, dysprosium ions and thulium ions.

[0020] Further, the laser filtering device is arranged between the second light polarization direction rotating device and the reflecting device.

[0021] The application has the advantages and positive effects that: the application utilizes the light polarization direction rotating device and the polarizer to realize the oscillation of the multi-longitudinal mode low-noise linear polarization base frequency laser, realizes the generation of the frequency-doubled laser through the in-cavity laser frequency conversion device, and finally outputs the stable frequency-doubled laser through the cavity mirror. The application has the characteristics of small size and low cost. Different waveband frequency-doubled lasers can be outputted by replacing different laser filtering devices and bidirectional optical amplifiers. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a structure schematic diagram of a cavity frequency-doubled optical fiber laser of the application using backward pumping.

[0023] Figure 2 It is a structure schematic diagram of another cavity frequency-doubled optical fiber laser of the application using backward pumping.

[0024] Figure 3 It is a structure schematic diagram of a cavity frequency-doubled optical fiber laser of the application using forward pumping.

[0025] Figure 4 It is a structure schematic diagram of another cavity frequency-doubled optical fiber laser of the application using forward pumping.

[0026] Figure 5 It is a structure schematic diagram of a cavity frequency-doubled optical fiber laser of the application using bidirectional pumping.

[0027] Figure 6 It is a structure schematic diagram of another cavity frequency-doubled optical fiber laser of the application using bidirectional pumping.

[0028] In the figure: 1, laser cavity mirror; 2, laser frequency-doubled device; 3, polarizer; 4, first light polarization direction rotating device; 5, first optical fiber collimator; 6, bidirectional optical amplifier; 7, first optical combiner; 8, first pump source; 9, second optical fiber collimator; 10, polarization splitting device; 11, second light polarization direction rotating device; 12, laser filtering device; 13, reflecting device; 14, second pump source; 15, second optical combiner. DETAILED DESCRIPTION

[0029] The application will be described in detail below with reference to the drawings and in conjunction with embodiments, it should be understood that the preferred embodiments described herein are only used to illustrate and explain the application, and are not used to limit the application.

[0030] In the description of the application, the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and do not require the application to be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation of the application. The terms "connected", "connected" used in the application should be understood broadly, for example, it can be fixed connection, or detachable connection; it can be directly connected, or indirectly connected through intermediate parts, and the specific meaning of the above terms can be understood by those skilled in the art according to the specific circumstances.

[0031] Please refer to Figures 1 to 6 An intracavity frequency-doubled fiber laser comprises a pump source, an optical combiner and a bidirectional optical amplifier 6, a first optical fiber collimator 5, a first optical polarization direction rotating device 4, a polarizer 3, a laser frequency doubling device 2 and a laser cavity mirror 1 are sequentially arranged along the optical path on one side of the bidirectional optical amplifier 6; a second optical fiber collimator 9, a polarization beam splitting device 10, a second optical polarization direction rotating device 11 and a reflecting device 13 are sequentially arranged along the optical path on the other side of the bidirectional optical amplifier 6.

[0032] The pump source is used to generate pump light.

[0033] The optical combiner is used to couple the pump light to the bidirectional optical amplifier 6.

[0034] The bidirectional optical amplifier 6 is used to absorb the pump light and generate and amplify the fundamental frequency laser.

[0035] The first and second optical fiber collimators are used to collimate the laser.

[0036] The first and second optical polarization direction rotating devices are used to rotate the polarization direction of the fundamental frequency laser by 45° in a non-reciprocal manner.

[0037] The polarizer 3 is used to pass only the fundamental frequency laser of one polarization direction; the laser cavity mirror 1 is used to make the fundamental frequency laser turn back and output the frequency-doubled laser.

[0038] The laser frequency doubling device 2 is used to make the fundamental frequency laser with a frequency of ω become a frequency-doubled laser with a frequency of 2ω after passing through, and separate the fundamental frequency laser and the frequency-doubled laser.

[0039] The polarization beam splitting device 10 is used to divide the fundamental frequency laser into S-polarized light and P-polarized light.

[0040] The reflecting device 13 is used to reflect the fundamental frequency laser after it has passed through the second optical polarization direction rotating device 11.

[0041] Laser cavity mirror 1 is used to fold back the fundamental frequency laser and output frequency-doubled laser.

[0042] The laser cavity mirror 1 is coated with a fundamental frequency high-reflection film and a frequency-doubled light transmission film; the reflection device 13 is coated with a fundamental frequency high-reflection film; the pump source outputs pump light to the optical beam combiner; the polarization direction of the polarizer 3 is consistent with the optical axis direction of the laser frequency doubling device 2.

[0043] The pump light generated by the pump source is coupled to the bidirectional optical amplifier 6 by the optical combiner. The bidirectional optical amplifier 6 absorbs the pump light and generates, amplifies and outputs the fundamental frequency laser.

[0044] The fundamental frequency laser output from one side of the bidirectional optical amplifier 6 is collimated by the first fiber collimator 5 and then enters the first optical polarization direction rotation device 4. After being non-reciprocally rotated by 45° by the first optical polarization direction rotation device 4, it enters the polarizer 3. The polarized fundamental frequency laser with the same transmission axis as the polarizer 3 passes through the polarizer 3 and enters the laser frequency doubling device 2. In the laser frequency doubling device 2, part of the polarized fundamental frequency laser is converted into a frequency-doubled laser, which is output through the laser cavity mirror 1. The polarized fundamental frequency laser that is not converted into a frequency-doubled laser is reflected by the laser cavity mirror 1 along the original optical path, passes through the laser frequency doubling device 2 and the polarizer 3 in sequence, and then enters the first optical polarization direction rotation device 4. After being non-reciprocally rotated by 45°, it enters the bidirectional optical amplifier 6.

[0045] The fundamental frequency laser output from the other side of the bidirectional optical amplifier 6 is collimated by the second fiber collimator 9 and then enters the polarization beam splitter 10. After being transmitted by the polarization beam splitter 10, it enters the second optical polarization direction rotation device 11. After being non-reciprocally rotated by 45°, it enters the reflection device 13. After being reflected by the reflection device 13, it returns to the second optical polarization direction rotation device 11. After being non-reciprocally rotated by 45° again, it enters the polarization beam splitter 10. After being processed by the polarization beam splitter 10, it enters the bidirectional optical amplifier 6.

[0046] Preferably, after the fundamental frequency laser output from the bidirectional optical amplifier 6 is incident on the polarization beam splitter 10, the folding optical path between the polarization beam splitter 10, the second optical polarization direction rotation device 11, and the reflection device 13 can be U-shaped.

[0047] Preferably, the polarization beam splitter 10 can be composed of a prism A, a parallelogram prism and a prism B attached from top to bottom. The cross-sections of prism A and prism B can be right triangles or right trapezoids, and the angle between the inclined plane and the right angle plane of the two can be 45 degrees. The reflecting device 13 can be a 45° isosceles right prism.

[0048] Preferably, the first light polarization direction rotating device 4 and the second light polarization direction rotating device 11 can each comprise a Faraday rotator.

[0049] Preferably, the pump source, the light combiner and the bidirectional optical amplifier 6 can form a forward pumping or a backward pumping or a bidirectional pumping. Please refer to Figure 1 and Figure 2 , the first pump source 8, the first light combiner 7 and the bidirectional optical amplifier 6 form a backward pumping, also called a reverse pumping. Please refer to Figure 3 and Figure 4 , the second pump source 14, the second light combiner 15 and the bidirectional optical amplifier 6 form a forward pumping, also called a positive pumping. Please refer to Figure 5 and Figure 6 , the first pump source 8, the first light combiner 7, the second pump source 14, the second light combiner 15 and the bidirectional optical amplifier 6 form a bidirectional pumping.

[0050] Preferably, the polarizer 3 can be a Glan prism or a polarization beam splitter prism. The polarization direction of the Glan prism can be the same as the optical axis direction of the LBO and can be placed at 45° with the P polarization direction.

[0051] Preferably, the laser frequency doubling device 2 can comprise a frequency doubling crystal, and the matching mode of the frequency doubling crystal is a type I critical phase matching. The laser frequency doubling device 2 can adopt an LBO (lithium triborate large power ultraviolet frequency doubling crystal), and the matching mode of the LBO is a type I critical phase matching.

[0052] Preferably, the polarization beam splitting device 10 can be a polarization beam splitting prism group or a pure yttrium vanadate crystal.

[0053] Preferably, the bidirectional optical amplifier 6 can comprise a gain fiber, and the gain fiber is provided with gain ions, and the gain ions comprise any one or more of neodymium ions, erbium ions, germanium ions, praseodymium ions, holmium ions, europium ions, ytterbium ions, dysprosium ions and thulium ions. The bidirectional optical amplifier 8 can adopt a ytterbium ion doped optical fiber.

[0054] Preferably, a laser filtering device 12 for filtering out laser other than the central wavelength of the fundamental frequency laser can be arranged between the second light polarization direction rotating device 11 and the reflecting device 13. The laser filtering device 12 can adopt a filter.

[0055] The above-mentioned laser cavity mirror 1, laser frequency doubling device 2, polarizer 3, first light polarization direction rotating device 4, first optical fiber collimator 5, bidirectional optical amplifier 6, first light combiner 7, first pump source 8, second light combiner 14, second pump source 15, second optical fiber collimator 9, polarization beam splitting device 10, second light polarization direction rotating device 11, laser filtering device 12 and reflecting device 13 can each adopt a component or a structural assembly in the prior art, or adopt a component or a structural assembly in the prior art and adopt a conventional technical means to construct.

[0056] The working principle of the present application is further explained below with reference to one preferred embodiment shown in the drawings: Figure 1

[0057] Figure 1 A schematic diagram of a cavity frequency-doubled fiber laser with backward pumping (reverse pumping) used in the present application, comprising: a laser cavity mirror 1, a laser frequency-doubling device 2, a polarizer 3, a first light polarization direction rotating device 4, a first optical fiber collimator 5, a bidirectional optical amplifier 6, a first light combiner 7, a first pump source 8, a second optical fiber collimator 9, a polarization beam splitting device 10, a second light polarization direction rotating device 11, a reflecting device 13.

[0058] The first pump source 8, the first light combiner 7, and the bidirectional optical amplifier 6 constitute the backward pumping (reverse pumping). The pump source 8 emits pump light, which is incident to the first light combiner 7, and the first light combiner 7 couples the pump light to the bidirectional optical amplifier 6. After absorbing the pump light, the bidirectional optical amplifier 6 forms population inversion, which is used to generate and amplify the fundamental frequency laser. The fundamental frequency laser can be decomposed into P-polarized fundamental frequency laser and S-polarized fundamental frequency laser.

[0059] The first light polarization direction rotating device 4 and the second light polarization direction rotating device 11 use Faraday rotators. The polarizer is selected to be a Glan prism, which is placed with the same direction of the optical axis of the LBO and at 45° with the P-polarization direction. The laser frequency-doubling device 2 uses LBO (lithium triborate high-power ultraviolet frequency-doubling crystal), and the matching mode of the LBO is type I critical phase matching. The polarization beam splitting device 10 uses a polarization beam splitting prism group. The bidirectional optical amplifier 6 uses a ytterbium-doped optical fiber.

[0060] ​For P polarization base frequency laser: After the first optical fiber collimator 5, it is incident to the first light polarization direction rotating device 4, the first light polarization direction rotating device 4 is used for non-reciprocal clockwise rotation of 45° to the polarization direction of P polarization base frequency laser, the 45° base frequency laser after rotation is incident to the polarizer 3, the polarizer 3 is used for screening the polarization direction of base frequency laser, only the polarization base frequency laser with 45° to P polarization direction is transmitted, and then it is incident to the laser frequency doubling device 2, the polarization frequency-doubled laser is obtained after being doubled by the laser frequency doubling device 2, and then it is incident to the laser cavity mirror 1. Because the frequency doubling conversion process of the laser frequency doubling device 2 is not 100% conversion, part of the 45° polarization base frequency laser is not converted, and the 45° polarization base frequency laser not subjected to frequency doubling is reflected by the laser cavity mirror 1 according to the original light path, is incident to the first light polarization direction rotating device 4 after the laser frequency doubling device 2 and the polarizer 3, and the first light polarization direction rotating device 4 non-reciprocal clockwise rotates 45° to the polarization direction of the 45° base frequency laser, which becomes S polarization base frequency laser. The S polarization base frequency laser is incident to the polarization light splitting device 10 after the first optical fiber collimator 5, the bidirectional optical amplifier 6, the first light combiner 7 and the second optical fiber collimator 9, is reflected by the polarization light splitting device 10 and is transmitted from the upper half of the polarization light splitting device 10 and is incident to the second light polarization direction rotating device 11, the second light polarization direction rotating device 11 is used for non-reciprocal clockwise rotation of 45° to the polarization direction of the S polarization base frequency laser, the base frequency laser after polarization rotation of 45° is incident to the reflecting device 13, the reflecting device 13 is a 45° isosceles right prism, and the base frequency laser after polarization rotation of 45° is incident to the reflecting device 13 again after being reflected by the 45° isosceles right prism. The base frequency laser after polarization rotation of 45° becomes P polarization base frequency laser, the P polarization base frequency laser is incident from the lower half of the polarization light splitting device 10, is transmitted by the polarization light splitting device 10, and is amplified again after the second optical fiber collimator 9, the first light combiner 7 and the bidirectional optical amplifier 6. The P polarization base frequency laser is transmitted in the laser cavity again according to the above light path after the first optical fiber collimator 5, the base frequency laser oscillates between the laser cavity mirror 1 and the 45° isosceles right prism, and the frequency-doubled laser is continuously output from the laser cavity mirror 1.

[0061] For S polarization base frequency laser: After the first optical fiber collimator 5, it is incident to the first light polarization direction rotating device 4, the first light polarization direction rotating device 4 is used for non-reciprocal clockwise rotation of 45° to the polarization direction of S polarization base frequency laser, the 45° base frequency laser after rotation is incident to the polarizer 3, the polarizer 3 is used for screening the polarization direction of base frequency laser, only the polarization base frequency laser with 45° to P polarization direction is transmitted, and then it is incident to the laser frequency doubling device 2, the polarization frequency-doubled laser is obtained after being doubled by the laser frequency doubling device 2, and then it is incident to the laser cavity mirror 1. Because the frequency doubling conversion process of the laser frequency doubling device 2 is not 100% conversion, part of the 45° polarization base frequency laser is not converted, and the 45° polarization base frequency laser not subjected to frequency doubling is reflected by the laser cavity mirror 1 according to the original light path, is incident to the first light polarization direction rotating device 4 after the laser frequency doubling device 2 and the polarizer 3, and the first light polarization direction rotating device 4 non-reciprocal clockwise rotates 45° to the polarization direction of the 45° base frequency laser, which becomes S polarization base frequency laser. The S polarization base frequency laser is incident to the polarization light splitting device 10 after the first optical fiber collimator 5, the bidirectional optical amplifier 6, the first light combiner 7 and the second optical fiber collimator 9, is reflected by the polarization light splitting device 10 and is transmitted from the upper half of the polarization light splitting device 10 and is incident to the second light polarization direction rotating device 11, the second light polarization direction rotating device 11 is used for non-reciprocal clockwise rotation of 45° to the polarization direction of the S polarization base frequency laser, the base frequency laser after polarization rotation of 45° is incident to the reflecting device 13, the reflecting device 13 is a 45° isosceles right prism, and the base frequency laser after polarization rotation of 45° is incident to the reflecting device 13 again after being reflected by the 45° isosceles right prism. The base frequency laser after polarization rotation of 45° becomes P polarization base frequency laser, the P polarization base frequency laser is incident from the lower half of the polarization light splitting device 10, is transmitted by the polarization light splitting device 10, and is amplified again after the second optical fiber collimator 9, the first light combiner 7 and the bidirectional optical amplifier 6. The P polarization base frequency laser is transmitted in the laser cavity again according to the above light path after the first optical fiber collimator 5, the base frequency laser oscillates between the laser cavity mirror 1 and the 45° isosceles right prism, and the frequency-doubled laser is continuously output from the laser cavity mirror 1.

[0062] Figure 2The structure diagram of another cavity frequency-doubling fiber laser of the present application using backward pumping (reverse pumping) is shown in Figure 1 The laser filtering device 12 is added between the second light polarization direction rotating device 11 and the reflecting device 13 based on the structure shown in the figure.

[0063] Figure 3 The structure diagram of a cavity frequency-doubling fiber laser of the present application using forward pumping (forward pumping) is shown in the figure, which comprises a laser cavity mirror 1, a laser frequency-doubling device 2, a polarizer 3, a first light polarization direction rotating device 4, a first optical fiber collimator 5, a bidirectional optical amplifier 6, a second light combiner 14, a second pump source 15, a second optical fiber collimator 9, a polarization beam splitter 10, a second light polarization direction rotating device 11, and a reflecting device 13.

[0064] Figure 3 The second pump source 14, the second light combiner 15, and the bidirectional optical amplifier 6 form forward pumping (forward pumping) in the figure. Figure 1 The working principle of the cavity frequency-doubling fiber laser shown in the figure is basically the same as that of the cavity frequency-doubling fiber laser shown in

[0065] Figure 4 The structure diagram of another cavity frequency-doubling fiber laser of the present application using forward pumping (forward pumping) is shown in the figure, which is based on the structure shown in the figure. Figure 3 The laser filtering device 12 is added between the second light polarization direction rotating device 11 and the reflecting device 13 based on the structure shown in the figure.

[0066] Figure 5 The structure diagram of a cavity frequency-doubling fiber laser of the present application using bidirectional pumping is shown in the figure, which comprises a laser cavity mirror 1, a laser frequency-doubling device 2, a polarizer 3, a first light polarization direction rotating device 4, a first optical fiber collimator 5, a bidirectional optical amplifier 6, a first light combiner 7, a first pump source 8, a second light combiner 14, a second pump source 15, a second optical fiber collimator 9, a polarization beam splitter 10, a second light polarization direction rotating device 11, and a reflecting device 13.

[0067] Figure 5 The structure of the cavity frequency-doubling fiber laser shown in the figure is combined with the structure of the cavity frequency-doubling fiber laser with backward pumping shown in Figure 1 The structure of the cavity frequency-doubling fiber laser shown in the figure is combined with the structure of the cavity frequency-doubling fiber laser with forward pumping shown in Figure 3 The bidirectional pump is composed of the bidirectional optical amplifier 6, the first light combiner 7, the first pump source 8, the second light combiner 14, and the second pump source 15. Figure 1 The working principle of the cavity frequency-doubling fiber laser shown in the figure is basically the same as that of the cavity frequency-doubling fiber laser shown in

[0068] Figure 6 Another structure of the intracavity frequency-doubled fiber laser using bidirectional pumping for the present application is shown in Fig. 3, which is based on the structure shown in Fig. 2. Figure 5 The laser filtering device 12 is added between the second light polarization direction rotating device 11 and the reflecting device 13 based on the structure shown in Fig. 2.

[0069] The above-described embodiments are only used to illustrate the technical ideas and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and the patent scope of the present application cannot be limited only by the above-described embodiments, that is, any equivalent changes or modifications made according to the spirit disclosed by the present application still fall within the patent scope of the present application.

Claims

1. An intra-cavity frequency-doubled fiber laser, characterized by, It includes a pump source, an optical beam combiner, and a bidirectional optical amplifier. On one side of the bidirectional optical amplifier, along the optical path, a first fiber collimator, a first optical polarization direction rotation device, a polarizer, a laser frequency doubling device, and a laser cavity mirror are arranged in sequence. On the other side of the bidirectional optical amplifier, along the optical path, a second fiber collimator, a polarization beam splitter, a second optical polarization direction rotation device, and a reflection device are arranged in sequence. The first and second optical polarization direction rotation devices are used to non-reciprocally rotate the polarization direction of the fundamental frequency laser by 45°. A laser frequency doubling device is used to convert a fundamental frequency laser with a frequency of ω into a frequency-doubled laser with a frequency of 2ω. A polarization beam splitter is used to separate fundamental frequency laser light into S-polarized light and P-polarized light; The pump light generated by the pump source is coupled to a bidirectional optical amplifier by an optical combiner. The bidirectional optical amplifier absorbs the pump light and generates, amplifies, and outputs the fundamental frequency laser. The fundamental frequency laser output from one side of the bidirectional optical amplifier is collimated by the first fiber collimator and then enters the first optical polarization direction rotation device. After being non-reciprocally rotated by 45°, it enters the polarizer. The polarized fundamental frequency laser with the same direction as the transmission axis of the polarizer passes through the polarizer and enters the laser frequency doubling device. Part of the polarized fundamental frequency laser is converted into a frequency-doubled laser and output through the laser cavity mirror. The polarized fundamental frequency laser that is not converted into a frequency-doubled laser is reflected back by the laser cavity mirror along the original optical path, passes through the laser frequency doubling device and the polarizer in sequence, and then enters the first optical polarization direction rotation device. After being non-reciprocally rotated by 45°, it enters the bidirectional optical amplifier. The fundamental frequency laser output from the other side of the bidirectional optical amplifier is collimated by the second fiber collimator and then enters the polarization beam splitter. After being transmitted by the polarization beam splitter, it enters the second optical polarization direction rotation device, is non-reciprocally rotated by 45°, and then enters the reflection device. After being reflected by the reflection device, it is folded back to the second optical polarization direction rotation device, is non-reciprocally rotated by 45° again, and then enters the bidirectional optical amplifier in sequence through the polarization beam splitter and the second fiber collimator.

2. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, After the fundamental frequency laser output from the bidirectional optical amplifier is incident on the polarization beam splitter, the folded optical path between the polarization beam splitter, the second optical polarization direction rotation device, and the reflection device is U-shaped.

3. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, The polarization beam splitter consists of prism A, parallelogram prism and prism B attached from top to bottom. The cross-sections of prism A and prism B are right triangles or right trapezoids, and the angle between their inclined planes and right angles is 45 degrees. The reflecting device is a 45° isosceles right prism.

4. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, Both the first and second optical polarization direction rotation devices include a Faraday rotator.

5. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, The pump source, optical combiner, and bidirectional optical amplifier form a forward pump, a backward pump, or a bidirectional pump.

6. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, The polarizer is a Glan prism or a polarizing beam splitter.

7. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, The laser frequency doubling device includes a frequency doubling crystal, and the matching method of the frequency doubling crystal is type I critical phase matching.

8. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, The polarization beam splitter is a polarization beam splitter prism assembly or a pure yttrium vanadate crystal.

9. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, The bidirectional optical amplifier includes a gain fiber, in which gain ions are provided. The gain ions include any one or more of neodymium ions, erbium ions, germanium ions, praseodymium ions, holmium ions, europium ions, ytterbium ions, dysprosium ions, and thulium ions.

10. The intra-cavity frequency-doubled fiber laser of claim 1, wherein, A laser filtering device for filtering out laser light other than the central wavelength of the fundamental frequency laser light is provided between the second light polarization direction rotating device and the reflecting device. A laser filtering device for filtering out laser light other than the central wavelength of the fundamental frequency laser light is provided between the second light polarization direction rotating device and the reflecting device.

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